MOLECULAR-STRUCTURE OF THE METHOXY-IRON(III) DERIVATIVE OF -HYDROXY-3,3'-DIAMIDOBIPHENYL)-DIPHENYL)-PORPHYRIN AND CO BINDING-PROPERTIES OF IRON(II)-PYRIDINE COMPLEXES OF 2,2'-SUBSTITUTED BIPHENYL STRAPPED PORPHYRINS
L. Prevot et al., MOLECULAR-STRUCTURE OF THE METHOXY-IRON(III) DERIVATIVE OF -HYDROXY-3,3'-DIAMIDOBIPHENYL)-DIPHENYL)-PORPHYRIN AND CO BINDING-PROPERTIES OF IRON(II)-PYRIDINE COMPLEXES OF 2,2'-SUBSTITUTED BIPHENYL STRAPPED PORPHYRINS, Inorganica Chimica Acta, 283(1), 1998, pp. 98-104
The molecular structure of the methoxy-iron(III) derivative \1(Me,OH)-
Fe(OMe)\ of the strapped porphyrin (5,15-(o,o' '-hydroxy-3,3'diamidobi
phenyl)-diphenyl)-porphyrin (I(Me,OH)) is reported. The 2-methyl-2'-hy
droxy-substituted biphenyl unit and the porphyrin ring are covalently
bound together by two amido-groups linking the 3,3'-positions of the b
iphenyl strap to two ortho-positions of the two meso-phenyl rings belo
nging to the 5,15-diphenylporphyrin. The iron(III) center present in \
1(Me,OH)-Fe(OMe)\ is five-coordinate, high-spin (S=5/2). It is bonded
to the four porphyrinato-nitrogens and the oxygen atom of the methoxy
group. The mean-value of the four Fe-N-p distances is 2.060(4) Angstro
m. The Fe-O bond length with the axial methoxy ligand is 1.867(3) A. T
he porphyrin core is both domed and ruffled. The doming is small, wher
eas the ruffling is more pronounced. The dihedral angle of the two phe
nyl moieties belonging to the biphenyl strap lies close to 105 degrees
. The orientation of the entire strap lying over the porphyrin core is
probably mainly determined by a strong hydrogen bond of 2.531(5) A li
nking the 2'-hydroxy group of the strap and the methoxy-oxygen bonded
to the iron atom. This oxygen atom of the 2'-hydroxy strap substituent
is also hydrogen bonded to the NH (N50) moiety of an amido group link
ing covalently the strap to the porphyrin. The binding of carbon monox
ide to five-coordinate iron(II)-pyridine complexes of such porphyrins
\1(Me,OH)-Fe(py)\ and \2(Me,OH)-Fe(py)\ (py = pyridine) has been explo
red. These carbonyl adducts \1(Me,OH)-(FeCO)-C-II(py)\ and \2(Me,OH)-(
FeCO)-C-II(py)\ display, respectively, in THF and in KBr pellets, two
v((CO)-C-12) stretching vibrations at 1966, 1944 and 1965 and 1938 cm(
-1), respectively. The occurrence of two v((CO)-C-12) stretching vibra
tions indicates the presence of two Fe-C-O conformers in both compound
s. However, these two carbonyl adducts enriched with (CO)-C-13 display
only a single (CO)-C-13 NMR signal lying at 208.1 and 208.0 ppm, resp
ectively. This result indicates that the two Fe-C-O conformers present
in \1(Me,OH)-Fe-II(CO) (py)\ and \2(Me,OH)(FeCO)-C-II(py) I interconv
ert more rapidly than the NMR time scale. Moreover, an almost linear c
orrelation is observed between the v((CO)-C-12) stretching vibrations
and the C-13 chemical shifts of the (CO)-C-13 NMR signals in a series
of iron(II) carbonyl adducts in which the second axial ligand of iron
is pyridine, \1(Me,OH)Fe((CO)-C-13) (py)\ and \2(X,Y)-Fe((CO)-C-13) (p
y)\[(X,Y)=(Me,OH), (Me,OMe), (H,H), (Me,Me), (OMe,OMe) and (NO2,NO2)].
In these carbonyl adducts, the v((CO)-C-12) stretching vibrations vary
between 1938 and 1987 cm(-1) and the chemical shifts delta(C-13) Of t
he C-13 NMR signals range from 202.5 to 208.1 ppm (versus TMS). Values
of delta(C-13) as large or larger than 208 ppm are observed in myoglo
bins and hemoglobins of various origins and in peroxidases in which th
e second axial ligand of iron is a histidine. Although an involvement
of a hydrogen bond between a distal histidine residue and the coordina
ted CO molecule in the large chemical shifts of the (CO)-C-13 NMR sign
als observed in these hemeproteins has been excluded, our model compou
nds, in which the axial ligand trans to CO is held constant, seem to i
ndicate that the polarity of the 2'-OH biphenyl substituent of the por
phyrin strap plays a role in the large chemical shifts of the (CO)-C-1
3 NMR signals observed in II(Me,OH)-Fe((CO)-C-13) (py) I and \2(Me,OH)
-Fe((CO)-C-13)(py)\. (C) 1998 Elsevier Science S.A. All rights reserv
ed.